I think either A.juliana or A.keraudreni although this one is not feeding on browns.

This one was approx 70mm when not stretched out.

Found in the shallow part (under 400mm depth) of a very large rock pool (min 100 square metres) exposed from approx 1 1/2 hours after the high tide which is completely cut off from the ocean then so still, clear waters.

Another interesting find @pjd1

The location name is not accurate - Reason